Inexpensive fiber optic attenuation

ABSTRACT

An attenuator for fiber optic cable has a device for receiving a length of the cable. A series of attenuation structures is defined on the device, the attenuation structures being located proximate to each other. Each of the attenuation structures is adapted to bend the cable through a corresponding arc to alter the path of the fiber optic cable so that a signal traveling through the fiber optic cable is attenuated. Additionally, the attenuation structures are individually accessible to select a desired amount of attenuation.

FIELD OF THE INVENTION

[0001] This invention relates to fiber optic attenuators.

BACKGROUND

[0002] Modern information networks having optical interconnects utilizevariable fiber optic attenuators. For example, in wave divisionmultiplex optical networks having increased wavelength content andgreater functionalities, optical communication channels may be added,dropped, and/or rerouted to any node of the network. As a result of thisflexibility, the network is more complex from an optical content pointof view. It is important to carefully monitor the optical power andindividual wavelengths channeled as a result. Otherwise, high errorrates may occur during propagation through communication channels havingoptical amplifiers (add-drop modules, multiplexers/demultiplexers, andother optical signal condition components). Consequently, inexpensive,reliable devices to adjust the power level of the applicable signals forhigher accuracy and higher repeatability are needed.

[0003] In general, optical communication systems include several opticalfiber-coupled devices (e.g., light sources, photodetectors, switches,attenuators, amplifiers, and filters). In the optical communicationssystems, the optical fiber-coupled devices transmit optical signals.Some optical signals that are transmitted in the optical communicationssystems have varying wavelengths or frequencies. The optical signals'different wavelengths transmit digital or analog data.

[0004] Several optical communication systems are lossy, i.e., theoptical fibers used therein scatter or absorb portions of the opticalsignals transmitted therealong (about 0.1-0.2 dB/km). The powerassociated with the optical signals is reduced when portions of theoptical signals transmitted on the optical fibers are scattered orabsorbed. Positioning amplifiers in the optical communication systemcompensates for power reductions attributable to the optical fibers. Byutilizing optical amplifiers, the power of the optical signalstransmitted along the optical fibers increases.

[0005] Power variations between the different wavelengths of the opticalsignals may occur after the optical signals propagating along theoptical fiber experience multiple cycles of power losses followed byamplification. If uncorrected, these power variations may cause adjacentwavelengths to interfere with each other, resulting in transmissionerrors.

[0006] When using fiber optic systems, specific control of opticalsignal levels entering various system components is often required. Ingeneral, optical attenuators are used to control the power variationsbetween the different optical signal wavelengths in opticalcommunication systems. For example, one method of controlling theoptical signal levels is to use an attenuator. An adjustable attenuatorallows the desired level of attenuation to be set and remain stable withtime, temperature, etc. Some optical attenuators control the powervariations between the different optical signal wavelengths byreflecting portions of specified optical signal wavelengths providedthereto.

[0007] Many optical attenuators include a plate attached to a substratewith torsional members, e.g., rods, springs. The plate is coated with areflective material. By applying a torque to the torsional members, theplate is moveable relative to the substrate. The movement of the plateattenuates optical signals provided thereto by reflecting portionsthereof away from the transmission path of the optical communicationsystem.

[0008] One problem with optical attenuators that include reflectiveplates relates to their insertion loss. Optical attenuators, in an “off”state, typically reflect optical signals with near zero attenuation.Near zero attenuation in the “off” state requires that the reflectiveplates have very flat surfaces. Reflective plates with very flatsurfaces are difficult to fabricate.

[0009] Also, near zero attenuation in the “off” state requires that theplane of the reflective plate be positioned parallel to the substrate.However, for a torsional plate structure, the torsional members arefragile such that the equilibrium rotation of the reflective platepotentially drifts after each “on/off” cycle. Such drifting of thereflective plate affects its position plate relative to the substrate.

[0010] Controlling the optical signal levels entering various systemcomponents is important to prevent transmission errors. This isespecially true in short distance runs, where more loss of the signal isneeded to prevent transmission errors.

[0011] Thus, optical attenuators continue to be sought.

SUMMARY OF THE INVENTION

[0012] An attenuator for fiber optic cable includes a device forreceiving a length of fiber optic cable. A series of attenuationstructures are defined on the device and are located proximate to eachother. Each of the attenuation structures is adapted to bend the cablethrough a corresponding arc to alter the path of the fiber optic cableso that a signal traveling through the fiber optic cable is attenuated.

[0013] In one version, the attenuation structures are individuallyaccessible to select a desired amount of attenuation. In anotherversion, the attenuator has a housing adapted to enclose a portion ofthe fiber optic cable. Extending inside and outside of the housing are aplurality of mechanisms moveably mounted to the housing. The mechanismsare moveable between a first, disengaged position and a second positionengaging the fiber optic cable at a corresponding location thereon. Thesecond position bends the fiber optic cable through a corresponding arcto alter the path of the fiber optic cable so that a signal travelingthrough the fiber optic cable is attenuated, but it does not cause thebending of the cable to exceed the cable's bend radius.

[0014] In still another embodiment, an attenuator has a grooved cylinderwherein the groove comprises a spiral and is sized to receive a fiberoptic cable. A means for securing the fiber optic cable to the groovedcylinder is provided.

BRIEF DESCRIPTION OF THE DRAWINGS

[0015]FIG. 1 is a side sectional view of one of the preferredembodiments of the invention with a fiber optic cable in place.

[0016]FIG. 2 is an enlarged end view of one of plungers of theembodiment of FIG. 1.

[0017]FIG. 3 is an enlarged, side elevational view of the plunger ofFIG. 2.

[0018]FIG. 4 is a perspective view of an alternative embodiment of theinvention.

[0019]FIG. 5 is a cross-sectional side view along line 5-5 of theembodiment shown in FIG. 4.

[0020]FIGS. 6 and 7 are perspective views of another alternativeembodiment of the invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0021] While the specification concludes with claims particularlypointing out and distinctly claiming the subject matter which isregarded as the invention, the invention will now be further describedby reference to the following detailed description of preferredembodiments taken in conjunction with the above-described accompanyingdrawings.

[0022] Referring generally to the embodiment shown in FIGS. 1-3,attenuator 100 includes a device 98 for receiving a length of fiberoptic cable 114. Device 98, in turn, includes a series of attenuationstructures 96 formed or defined thereon and located proximate to eachother. Each of the attenuation structures 96 is adapted to bend fiberoptic cable 114 through a corresponding arc to alter its path so that asignal traveling through fiber optic cable 114 is attenuated.Attenuation structures 96 are individually accessible to select adesired amount of attenuation.

[0023] In the embodiment shown in FIG. 1, attenuator 100 includes ahousing 118 with opposite walls 122, 124, which housing 118 is adaptedto enclose a portion of fiber optic cable 114.

[0024] Attenuation structures 96 comprise a plurality of mechanisms 120which are mounted to housing 118 and movable between a first, disengagedposition and a second, engaged position. Mechanisms 120 are preferablyslidable individually from the first, disengaged position to the second,engaged position by pushing individual mechanisms 120 toward housing 118in the directions shown by arrows A (shown for two of the mechanisms120). Mechanisms 120 include heads 116 positioned at the ends of themechanisms 120 to engage fiber optic cable 114. Head 116 optionallyincludes additional means to retain cable 114 in position, here shown asgroove 126 (FIG. 2).

[0025] When moved to the second, engaged position, mechanism 120 bendsthe fiber optic cable 114 through a corresponding arc to alter the pathof fiber optic cable 114. The arc imposed on cable 114 attenuates thesignal traveling through the fiber optic cable.

[0026] Mechanism 120 is sized relative to cable 114 and mounted tohousing 118 so that, when in the second, engaged position, mechanism 120does not bend cable 114 beyond the cable's associated bend radius. Inparticular, base 102 of mechanism 120 optionally includes a flange 94located to oppose housing 118 and thereby limit the distance throughwhich mechanism 120 may be advanced inside of housing 118. In addition,radius of head 116 is preferably selected to be less than the bendradius of cable 114.

[0027] Detent, catch, or ratchet 104 locks mechanism 120 in its secondposition after mechanism 120 has been suitably pushed inside of housing118. Guides 106 optionally allow mechanisms 120 to slide relative tohousing 118 in predetermined paths perpendicular to opposite walls 120,122. Guides 106 and mechanisms 120 may also be structured to engage eachother in such a way to keep mechanisms 120 from being pulled completelyout of housing 118 and thus separated from the unit.

[0028] Head 116 of mechanism 120 is preferably rounded, as shown in FIG.3, having a suitable radius selected to bend that portion of the fiberoptic cable engaged by head 116 within the allowable bend radius. Groove118 is defined in bend 116 to have a width sufficient to receive thefiber optic cable 114 and is likewise provided with a radius suitable toreceive cable 114 within the allowable bend radius. The groove isoptionally shaped to engage cable 114 in a friction fit. Thus, head 116includes a structure to retain the fiber optic cable 114 in engagementtherewith. Alternate structures, not limited to a groove, can likewisebe used to retain the fiber optic cable 114 in engagement with head 116.

[0029] Mechanisms 120 are mounted along opposite walls 122, 124 atalternating locations to define corresponding, alternating bends infiber optic cable 114. Mechanisms 120 are sized and mounted to causeeach of the bends of the fiber optic cable to extend through an arc of180° when mechanisms 120 are in their second, advanced positions. It hasbeen found that a 180° arc generally attenuates the signal by ½ dB.Preferably, attenuator 100 comprises twelve, independently actuatablemechanisms 120. As such, attenuator 120 is able to attenuate a signalflowing through fiber optic cable 114 by an amount ranging from ½ dB to6 dB by moving a corresponding number of mechanisms 120 to the second,engaged position.

[0030] Mechanism 120 preferably comprises plungers 121 with respectivestems 128. The stems 128 of mechanism 120 have outer portions 102extending outwardly from housing 118 and inner portions 130 extendinginto the housing and secured to respective heads 116. When mechanisms120 are moved, stems 128 slide in corresponding bores in housing 118.

[0031] The interior of housing 118 is accessed preferably by havinghousing 118 separate along a suitable plane, such as in a clamshellfashion. For example, housing 118 shown in the embodiment of FIG. 4separates along boundary 402. Alternate approaches to accessing theinterior of housing 118 are also suitable, such as by separating the twoportions 120, 122 of housing 118 (FIG. 1) along a plane corresponding toopenings 112 at the ends of the housing. In whatever manner housing 118is opened, once opened, fiber optic cable 114 is placed inside ofhousing 118. The cable 114 enters and exits housing 118 through holes112.

[0032] Referring now to FIGS. 4-5, attenuator 400 has a device 498similar to device 98 of the embodiment of FIGS. 1-3; however, attenuator400 includes a cam system 406 for actuating multiple mechanisms 404 by asingle operation. Cam system 406 makes use of two sets 418 of rotatablecams 408, one set mounted proximate to one side of device 498 and asecond set (not shown) mounted proximate to the opposite side of device498. For each set 418, cams 408 are mounted to shaft 420 to rotatetogether in the directions of arrows B, to engage the opposing ends 422of mechanisms 404 and advance them toward housing 424. System 406contains a locking device which prevents mechanisms 404 from sliding ormoving out of position. When such a system is implemented, mechanisms404 can have either a first and second position, or, alternatively, theymay be moved gradiantly by appropriate rotation of cams 408.

[0033] Another alternative embodiment of the invention is depicted inFIGS. 6 and 7. Referring generally to FIGS. 6-7, attenuator 600 includesa device 698 for receiving a length of fiber optic cable 608. Device698, in turn, includes a series of attenuation structures 696 formed ordefined thereon and located proximate to each other. As with theprevious embodiments, each of the attenuation structures 696 is adaptedto bend fiber optic cable 608 through a corresponding arc to alter itspath so that a signal traveling through fiber optic cable 608 isattenuated. Attenuation structures 696 are individually accessible toselect a desired amount of attenuation.

[0034] In this embodiment, device 698 is in the form of a cylinder 602,and the attenuation structures 696 are in the form of a spiral groove604 defined around cylinder 602 and sized to receive fiber optic cable608. Otherwise stated, each 360- or 180-degree arc or “winding” ofspiral groove 604 comprises one of the attenuation structures 696 inthis embodiment. Attenuation is achieved by wrapping fiber optic cable608 around cylinder 602 in spiral groove 604 a selected number of times.

[0035] Means for securing the fiber optic cable 608 to the groovedcylinder 602 is also provided, here shown as sleeve or wrap 610,although alternate means are suitable to perform this function. Thesleeve or wrap 610 is removably secured to cylinder 602 by any suitablemeans, such as, but not limited to, Velcro®, a rubber sheath, oradhesive tape.

[0036] Cylinder 602 includes a longitudinal groove 606 runningperpendicular to and between the spirals of groove 604. Once the desiredamount of attenuation is achieved, cable 608 is placed into longitudinalgroove 606 and extended out the end of cylinder 602.

[0037] Wrapping fiber optic cable 608 into spiral groove 604 aroundcylinder 602 bends cable 608 through a predetermined arc. Because of thebending or spiraling of the cable 608, the signal flowing through cable608 is attenuated. Thus, varying the number of winds of the cable ingroove 604 varies the amount of attenuation and attenuation in the rangeof ½ dB to 6 dB can easily be achieved. In view of this, the signalflowing through the fiber optic cable 608 is attenuated more in FIG. 6than in FIG. 7 because fiber optic cable 608 in FIG. 6 is wrapped moretimes around cylinder 602.

[0038] Grooves 604, 606 have widths sufficient to receive fiber opticcable 602 therein. Cylinder 602 is made out of any material suitable forthe purposes described above, one such material being a resilientlycompressible, polymeric material.

[0039] Groove 604 and longitudinal groove 606 may themselves beconfigured to secure cable 608 to cylinder 602. For example, the outeredge of grooves 604, 606 may include a lip 612 of resilientlycompressible material. Lip 612 is deflected upon insertion of cable intogrooves 604, 606, and returns to at least partly “cover” grooves 604,606 to retain cable 608 therein.

[0040] In addition to the advantages apparent from the foregoingdescription, the attenuator of the present invention is structured sothat the fiber optic cable does not have to be cut in order to attenuatethe signal flowing therethrough.

[0041] As another advantage, an input or an output does not have to beconnected to the fiber optic attenuator.

[0042] As still another advantage, it is not necessary to interpose adevice in the signal path of the fiber optic cable; rather, the cableremains uninterrupted in the present invention.

[0043] Additional advantages and variations will be apparent to thoseskilled in the art, and those variations, as well as others which skillor fancy may suggest, are intended to be within the scope of the presentinvention, along with equivalents thereto, the invention being definedby the claims attended hereto.

What is claimed is:
 1. An attenuator for fiber optic cable comprising: adevice for receiving a length of the cable; a series of attenuationstructures defined on the device and located proximate to each other;each of the attenuation structures adapted to bend the cable through acorresponding arc to alter the path of said fiber optic cable so that asignal traveling through the fiber optic cable is attenuated, theattenuation structures being individually accessible to select a desiredamount of the attenuation.
 2. The attenuator of claim 1, wherein theseries of attenuation structures is sufficient to attenuate the signalby any selected amount in the range of ¼ dB to 6 dB.
 3. The attenuatorof claim 1, wherein the attenuation structures comprise mechanismsmoveably mounted to the device, the mechanisms being moveable between afirst, disengaged position and a second position engaging the fiberoptic cable at a corresponding location thereon, the second positionbending the fiber optic cable through the corresponding arc, themechanisms sized and mounted so that, in the second position, theengagement of the cable does not cause the bending of the cable toexceed the bend radius of the cable.
 4. The attenuator of claim 1,wherein the attenuation structure comprises a groove comprising a spiraland sized to receive a fiber optic cable therein.
 5. An attenuator forfiber optic cable comprising: a housing adapted to enclose a portion ofthe fiber optic cable, the fiber optic cable having a corresponding bendradius; and a plurality of mechanisms moveably mounted to said housing,the mechanisms being moveable between a first, disengaged position and asecond position engaging the fiber optic cable at a correspondinglocation thereon, the second position bending the fiber optic cablethrough a corresponding arc to alter the path of said fiber optic cableso that a signal traveling through the fiber optic cable is attenuated,the mechanisms sized and mounted so that, in the second position, theengagement of the cable does not cause the bending of the cable toexceed the bend radius.
 6. The attenuator of claim 5, wherein themechanisms have rounded heads positioned on the mechanisms to engage thefiber optic cable.
 7. The attenuator of claim 6, wherein said headsinclude structures to retain the fiber optic cable in engagementtherewith.
 8. The attenuator of claim 7, wherein the structure comprisesa groove defined in the head, the grooves having widths sufficient toreceive the fiber optic cable therein.
 9. The attenuator of claim 5,wherein each of the mechanisms comprises a plunger mounted at spacedlocations along the housing, the plunger having a stem and a headdefined therein, the stem having an outer portion extending outwardlyfrom the housing and an inner portion extending into the housing andsecured to the head.
 10. The attenuator of claim 9, wherein the plungersare slidably mounted, the plungers being manually moveable between thefirst and second positions by pushing or pulling the outer portions withrespect to the housing.
 11. The attenuator of claim 10, wherein themechanisms include ratchets for retaining the plungers in theirrespective second positions.
 12. The attenuator of claim 5, wherein thehousing has opposite walls extending longitudinally, and the mechanismsare mounted along the opposite walls at alternating locations to definecorresponding, alternating bends in the fiber optic cable.
 13. Theattenuator of claim 12, wherein the mechanisms are sized and mounted tocause each of the bends of the fiber optic cable to extend through anarc of substantially 180 degrees.
 14. The attenuator of claim 1l,comprising twelve of the mechanisms, each of the mechanisms beingindependently actuatable, whereby the attenuator is able to attenuatethe signal by an amount ranging from ½ dB to 6 dB by moving acorresponding number of the mechanisms to the second position.
 15. Theattenuator of claim 5, wherein the housing has opposite ends throughwhich the cable enters and exits, the ends defining a chamber sized toreceive the portion of the fiber optic cable without interruptionthereof, the mechanisms located between the opposite ends and notinterrupting the cable when engaged therewith.
 16. An attenuator forfiber optic cable, comprising: a cylinder with a groove defined therein,the groove comprising a spiral and sized to receive a fiber optic cabletherein; means for securing said fiber optic cable to said cylinder. 17.The attenuator of claim 16, wherein said means for securing said fiberoptic cable to said cylinder comprises a lip in operative proximity tothe groove.
 18. The attenuator of claim 16, wherein the securing meanscomprises a wrap sized to surround the cylinder.
 19. An apparatus forattenuating a length of fiber optic cable comprising: a housingconfigured to receive said length of fiber optic cable having an amountof attenuation associated therewith; a plurality of attenuationstructures on said housing, said plurality of attenuation structuresbeing configured to abut said length of fiber optic cable; andadjustment means for adjusting said plurality of attenuation structuresto alter an optical path of said length of fiber optic cable and varysaid amount of attenuation.
 20. The apparatus according to claim 19,wherein each of said plurality of attenuation structures is individuallyadjustable.
 21. The apparatus according to claim 20, wherein saidadjustment means comprises a screw mechanism configured to product abend in said length of fiber optic cable.
 22. The apparatus according toclaim 20, wherein said adjustment means comprises a plurality of screwmechanisms configured to produce a plurality of bends in said length offiber optic cable, wherein adjacent ones of each of said plurality ofscrew mechanisms abut said length of fiber optic cable from differentdirections.
 23. A method of attenuating a length of fiber optic cablecomprising: mounting said length of fiber optic cable in a housing, saidlength of fiber optic cable having an amount of attenuation associatedtherewith; abutting the length of fiber optic cable with a plurality ofattenuation structures; and varying the amount of attenuation of saidlength of fiber optic cable by adjusting the plurality of attenuationstructures to alter an optical path of said length of fiber optic cable.